The desire for whiter, lighter teeth is considered to be desirable in today's cosmetically oriented society. The tooth structures which are affected by stains are the enamel and dentin, and the thin layer on the enamel surface, the acquired pellicle. Teeth can become discolored with age, blood, amalgam restorations, antibiotics such as tetracycline, and substances in food, beverages and tobacco and salivary fluid.
Tooth stains are generally classified as either extrinsic or intrinsic depending on whether the stain is on the surface of the tooth, within the acquired pellicle or within the tooth structure itself within the enamel or dentin. Extrinsic staining of the acquired pellicle can occur from foods or compounds, which contain toxins and other polyphenolic chemicals on the surfaces of the teeth. Intrinsic staining, on the other hand, occurs when chromogens and pre-chromogens penetrate the enamel and dentin and become tightly bound to the tooth structure. Intrinsic staining can occur when blood or amalgam products leach into the enamel and dentin. Intrinsic staining is not removed by mechanical means such as tooth cleaning and generally requires the use of chemicals, for example strong oxidizing agents such as hydrogen peroxide that can penetrate into the tooth structure to effect a change in the light absorbability of the stain chromogen and or solubility of the chromogen.
Tooth bleaching is generally accomplished by gels, pastes or liquids which contain an oxidizing agent such as hydrogen peroxide. The products from the breakdown of hydrogen peroxide, the oxygen free radicals, attach to the chromogen molecules, making them colorless and/or water soluble, allowing the tooth to appear lighter and brighter.
The most commonly used oxidizing agent is hydrogen peroxide, commonly obtained from carbamide peroxide which is mixed with an anhydrous viscous carrier containing glycerin and/or propylene glycol and/or polyethylene glycol. When in contact with water, carbamide peroxide dissociates into urea and hydrogen peroxide. The hydrogen peroxide, in the presence of water, dissociates into water and an oxygen free radical species. It is these species of highly reactive oxygen anions, which react with a stain molecule making the stain more water soluble transparent or both. This is what is responsible for teeth appearing lighter and brighter; i.e., the desired tooth whitening.
There are several consumer-based delivery systems to deliver the carbamide peroxide to the surfaces of the teeth. A common approach is to have a pre-made plastic tray. The oxidizing agent in a gel form is dispensed into the plastic tray by the consumer and the tray is worn over the teeth intermittently for a period of two weeks to several months. This approach can be cumbersome since the trays are often uncomfortable to wear and in many cases do not fit adequately causing discomfort.
Another approach is to simply paint on the oxidizing agent, carbamide peroxide, or hydrogen peroxide directly on the teeth. These products have the inherent problem of being easily removed by the lips, or tongue from the tooth surfaces which significantly reduces their effectiveness.
A common approach is to incorporate the oxidizing agent in a strip, such as shown in U.S. Pat. No. 5,891,453, and have the consumer wear the strip intermittently over a period of two weeks. These strips have the inherent problem of contacting the teeth only on the facial surfaces, as opposed to the difficult to reach interproximal surfaces, between the teeth, where most of the stain is present. Another problem with these strips is that the strips tend to slip of the tooth causing discomfort for the user.
To overcome the problems inherent in the over the counter strips, trays and paint-on products, there is a need for a relatively inexpensive and effective moldable tray which can more readily reach the interproximal areas of the teeth and be comfortable and easy for the consumer to apply and wear.